This invention is directed generally to electromechanical devices and, more specifically, to a switching mechanism used in a circuit breaker.
Electrical devices, such as circuit breakers, are used in many residential, commercial, and industrial electric systems, being indispensable components of such systems in protecting against over-current conditions. In response to application-specific needs, such as response time, space constraints, efficiency, capacity, and type of reset function (manual or remote), a variety of different switching mechanisms for circuit breakers have been developed.
Some switching mechanisms focus on reducing the period of time that is required to switch the circuit breaker from an ON position to a TRIPPED position. In the ON position the circuit breaker allows current flow through a particular electrical circuit, while in the TRIPPED position the circuit breaker prevents the current flow. A faster switching mechanism allows a circuit breaker or other electrical device to perform at higher current levels, e.g., the circuit breaker can achieve a higher current-interrupt level.
For example, a prior art circuit breaker has a switching mechanism that includes a toggle link unit, which is connected to a trip lever and a carrier. The toggle link unit has two components connected by a center pin, an upper link and a lower link. The upper link is connected to the trip lever, wherein the trip lever, which is swingably supported at one end, is normally engaged with a tripping mechanism to prevent the trip lever from swinging. The lower link is connected to the carrier, wherein the carrier is rotatably supported by a switching shaft and has a movable blade. The moveable blade has a movable contact that, in the ON position, is in contact with a stationary contact. When a tripping condition occurs, e.g., the current level in an electrical device protected by the circuit breaker is higher than the accepted level for the circuit breaker, the trip lever is disengaged from the tripping mechanism and the switching mechanism is actuated. Specifically, the trip lever rotates in a counterclockwise motion causing a chain reaction that results in the movable contact being separated from the stationary contact. The motion of the upper link is directed in part by a separate piece, an interfering stopper, which attempts to move the upper link in a straight, rather than curved, path
However, a switching mechanism similar to the one described above has a number of drawbacks related to the size and the interrupt levels that the circuit breaker may achieve. For example, using the separate stopper has at least two drawbacks: it necessarily increases the size of the circuit breaker, and it adds an additional step during assembly. Less parts and less assembly steps generally result in a more compact, less expensive circuit breaker.
Another drawback is that the speed of the switching mechanism is slow, therefore limiting the current-interrupt levels that the circuit breaker could potentially achieve. Although the mechanism design attempts to minimize the rather large swing radius of the upper link, it nevertheless fails to continuously drive the upper link. The stopper does not provide continuous contact with the upper link that would result in a continuous driving force. A continuous driving force would result in a faster moving switching mechanism because it would keep the upper link moving at all times, and because it would direct the upper link to follow a more direct path than the path the upper link would normally follow.
Accordingly, there is a need for an improved switching mechanism which overcomes the above-mentioned and other drawbacks
Briefly, in accordance with the foregoing, the invention relates to a switching mechanism for use in an electromechanical device, such as a circuit breaker. The switching mechanism comprises a stationary contact, a blade assembly having a blade, which includes a movable contact, a frame guide having a guiding area, a trip lever, a tripping mechanism, a lower link, and an upper link. The trip lever is connected to the frame guide to cause the separation of the movable contact from the stationary contact, wherein the movable contact is in contact with the stationary contact in an ON position of the circuit breaker and is separated from the stationary contact in a TRIPPED position of the circuit breaker. The tripping mechanism is adapted for holding the trip lever in the ON position, wherein the tripping mechanism releases the trip lever to the TRIPPED position when a tripping condition occurs. The lower link has a first end and a second end, and is adapted for moving the blade between the ON and the TRIPPED positions. The first end is connected to the blade assembly. The upper link includes a lower link end, a trip lever end, and an interface area, wherein the lower link end is connected to the second end of the lower link, the trip lever end is connected to the trip lever, and the interface area is adapted to remain in continuous contact with the guiding area in the ON position, in the TRIPPED position, and while moving between the ON position and the TRIPPED position.
In one embodiment of the invention, the switching mechanism comprises an upper link that includes a first end adapted for connecting to a trip lever; a second end adapted for connecting to a lower link; a first slidably-engaging surface adapted for driving an initial motion of the upper link when a TRIPPING condition occurs; a second slidably-engaging surface adapted to continue driving the upper link after the first slidably-engaging surface has partially driven the upper link and until the switching mechanism is in a TRIPPED position; a clearance surface located between the first slidably-engaging surface and the second slidably-engaging surface; and a front surface located near the first end adapted for holding the upper link stopped in the TRIPPED position.
In another embodiment of the invention, the switching mechanism comprises a frame that includes a support structure and a guide structure. The guide structure is integrated to form a single component with the support structure, comprising an angled surface adapted for holding the switching mechanism in an ON position and for driving an initial motion of an upper link when a TRIPPING condition occurs; a ramp surface adapted to continue driving the upper link after the angled portion has partially driven the upper link and until the switching mechanism is in a TRIPPED position; and a resting surface adapted for holding the upper link stopped in the TRIPPED position.